In teaching a foreign language, and particularly for building a vocabulary, it is a common practice to use learning aids that match words or phrases in the foreign language with their counterparts in a student's native language. Most often used are simple cards having the foreign word or phrase written on one side and its translation written on the other side. It is also common to use parallel lists, either on a single sheet or on separate sheets. The list in the known language is usually covered while the words in the foreign language are studied. When unsure of the meaning of a word in the foreign language list, the student will briefly uncover the adjacent list in the known language to compare the foreign word with the known word.
For more advanced students, the parallel list concept has been expanded to complete books, in which the text is printed in one language in alternate columns or on alternate pages, for example on the even-numbered pages, and a translation of this text is printed in adjacent columns or on the alternate facing pages, for example on the odd-numbered pages. The translated text is positioned substantially opposite to the text in the first language, so that the counterpart words and phrases can be found by looking across from one column to the adjacent column or from one page to the opposite facing page.
Whether used for lists of characters, discrete words and phrases or for continuous coherent text, such as a story, the side by side arrangement described above requires the reader to shift focus laterally from one column or page to an adjacent column or page to check the meaning of words he does not know or has forgotten. The shifting of visual attention is a distraction, particularly when reading coherent text, so that much of the potential reinforcement to be obtained from the use of a duplicate text format is unrealized when using the side by side arrangement.
When presented with the side-by-side translation, the student will, after trying to comprehend the foreign-language text, inevitably come to rest his eyes on the version he is most familiar with, i.e., the translation. The side-by-side layout distracts the student from his initial intent which is to comprehend or study the foreign-language text.